What is the problem with my sound system?

We've got a new rig for our pa system. I'm a professional musician. We usually put a PreSonus Studiolive 16.4.2 into a sunn powered mixer to 2 sonic 8ohm pa speakers. We recently replaced the sunn with a crown XLS 602 power amp. I tested it out, and got no signal to the speakers. Do I need a preamp, or is there something else wrong?